Product for and process of treating metallic articles before coating



United States Patent PRODUCT FOR AND PRflCESS OF TREATING -METALLIC ARTICLES BEFORE COATING No Drawing. Application August as, 1951, Serial No. 244,109

Claims priority, application France July 12, 1946 22 Claims. (Cl. 252136) This application is a continuation-in-part of U. S. application, Serial No. 753,816, filed June 10, 1947, entitled Preparation of Metallic Surfaces Which Are To Be Painted, now abandoned.

It is an object of this invention to produce a product which carries out all three stages of the preparation of metallic surfaces for painting or re-painting in one step.

It is a further object of this invention to produce an industrial product for simultaneously degreasing, descaling or derusting and passivating metals in preparation for coating them.

It is a still further object of this invention to provide a process for the manufacture of the product to be used for the above-stated objects.

The preparation of metallic surfaces which are to be painted or repainted has generally been carried on in three stages: first degreasing, then removal of rust and scale and then passivation of the metal. Among the products used for the degreasing of metallic surfaces are organic solvents such as various hydrocarbons (particularly of a volatile nature), chlorinated derivatives of hydrocarbons, higher alcohols and hot alkaline liquors having emulsifying agents added thereto.

The descaling of steel is generally carried out in a solution containing hydrochloride, sulphuric or phosphoric acids. The descaling of aluminum is generally carried out in alkaline solution or in solutions of sulfochromic acid.

The step of passivation is generally carried out in chromic solutions i. e. those given in French Patent No. 966,785 (application No. 518,562 filed on July 12, 1946).

As stated above, it was previously necessary to carry on the preparation of the metals for painting or coating in the three above-mentioned steps. After each step the metal had to be washed, then dried or wiped off. It can therefore be seen that a product which can combine all three steps in one would be highly useful. It was the desire to produce such a product that led various inventors to try, unsuccessfully until thep resent time, to combine two or more of these steps into a single operation.

Some success was found in producing a solution which would at the same time degrease and descale or derust the metallic surface. Solutions containing phosphoric acid and butyl alcohol were used for this purpose. The major fault in such preparations lay in the fact that they do not readily mix because butyl alcohol is not completely miscible with water or aqueous solutions; for example, butyl alcohol is miscible with water in proportions of 90% to or 10% to 90% but is not miscible in any intermediate proportions. Such solutions which contain butyl alcohol in a greater amount and phosphoric acid in a lesser amount degrease well but descale poorly. Conversely, solutions which contain phosphoric acid in a greater amount and butyl alcohol in a lesser amount descale well but degrease poorly. Ethyl alcohol is rarely used for degreasing and is only used when admixed with butyl alcohol. The reason for the limited use of ethyl alcohol is that it is not a very good grease dissolvent and does not dissolve oils and fats except for the glycerides of acid alcohols, i. e. castor oil.

While it is true that solutions of'the above-mentioned type do render the metalpassive to a sufiicient degree, that is so only while the solution remains on the surface of the metal. When the solutions are removed from the surface i. e. by washing, the metal will sometimes rust or corrode again and it is then necessry to reclean the surface. If the surface is not recleaned, the metal will rust again and some grease along with products of the transformation of the rust or scale will to some extent remain on the surface of the metal. The desired coating i. e. paint will in such case not adhere well to the metal surface. To prevent this from happening an additional step of washing with hot water and immediately drying, was necessary before applying the paint, which paint had to be then applied as promptly as possible.

The present invention provides a new product which may be used for carrying out the degreasing, descaling and passivation of the metal in one step. The weakness of necessarily using a water-immiscible organic solvent such as butyl alcohol, because the water-miscible organic solvents are not good degreasers, is overcome by the present invention by the use of a substance which in aqueous solution is capable of emulsifying greases and detaching them from the metallic surface. The aqueous-organic solutions without the emulsifying agent would have too weak a degreasing effect to 'be used successfully. The term greases as herein used is also meant to include old dried paint, varnish, lacquer, etc. i

The term aqueous-organic solutions is used to cover liquid mixtures of water with water-miscible organic solvents. Any organic-solvent miscible with Water in all proportions may be used with the present invention. The following water-miscible organic solvents are preferred: methyl alcohol, ethyl alcohol (denatured alcohol being preferred for the sake of economy), glycerine, propyl alcohol, isopropyl alcohol and pyridine. Any of the above-mentioned organic solvents or mixtures of them may be used.

The following water-miscible organic solvents may also be used: glycol, and glycolic ether, acetone, acetal, these two latter being not very appropriate while too volatile.

In fact, any water-miscible organic solvent may be used though tests have proved the first-mentioned group to be the most effective.

The following emulsifiers for the aqueous-organic solutions may be used:

Monoethanolamine, diethanolamine, triethanolamine, and polyethanolamine, which is a mixture of the mono, di, and tri ethanolarnines, the most useful being tri and/ or poly ethanolamine. All of the above-mentioned ethanolamines are very strong bases with a pH of about 13, and can react with acid to form salts, for example, triethanolamine and phosphoric acid will react to form the following addition product:

wherein n is known to be 1 to 10 inclusive and may even be a fractional value. The formula cannot be written with any greater definiteness than the above because of the different amounts of phosphoric acid that canreact with the triethanolamine. Similar addition products of phosphoric acid with mono, di, and/ or polyethanolamine may be formed. a 1

It has been established that these acid addition prodnets of the ethanolamine havea strong emulsifyingaction and are useful in aqueous-organic solutions for degreasing metallic surfaces of such substances as greases, oils, remnants of old paint, etc.

The above is combined with an acid phosphate of chromium, yielding a double acid phosphate of chromium and the ethanolamine, which acid phosphate in this solution is a descaling and a derusting agent and at the same time a passivating agent by inhibiting attack on the underlying metal. A convenient means for carrying out this invention is to combine chromic phosphate with one of the ethanolamines, mono, di, tri, and/or poly. To carry out such combination it is of course necessary to have a pH of less than 3, otherwise a hydroxide of chromium will precipitate. It is possible within the scope of the present invention to use other acid phosphates such as those of zinc and manganese, etc. However, the chromic phosphate has been found to be by far the most useful and though the additions of zinc or manganese phosphates may to some extent aid in the descaling, they are not necessary. It is also possible to use the double acid phosphate of chromium and the ethanolamine in a simple aqueous solution without the use of a water-miscible organic solvent, provided that this solution is also kept within the pH limits required. Of major importance, however, is the use of the acid phosphate of chromium with the above-mentioned ethanolamines in aqueous-organic solutions. The pH of this solution must be between 0.5 and 3 and preferably between 1 and 2.5.

The preferred proportions of the final solution is within the following limits:

Ethanolamine (preferably poly or tri) 1 to 5%-preferably 2% Phosphate ion-l to 60%preferably 20% Aqueous-organic solvents (preferably an alcohol or pyridine) 5 to 20%-preferably Chromie ionl to 5%preferably 2% The more water the solution contains the better it will clean, but the less well it will degrease, and conversely the less water it contains the better it will degrease but the less well it will clean.

The greater the concentration of phosphate ions, the greater the concentration of chromium ions required in order to keep the pH within the limits of 0.5 to 3.0. In this solution the Cr+++ ion is in combination with phosphoric acid in the form of a double phosphate of chromium and of the ethanolamine, preferably poly or triethanolamine. It is difficult to distinguish between a phosphate and a double phosphate in this case because of the possible variations in the value of n, as previously mentioned. In any case, it is an acid phosphate. Some of the Water-miscible organic solvents used, such as alcohol, may in this acid solution form an acetal, so that the final solution will contain an acetal in addition to the other constituents.

The invention embraces in particular industrial produets for simultaneously degreasing, descaiing or derusting and passivating, produced in the form of a solution containing bodies capable of giving these three actions. An excellent solution made by the present invention contains for example, triethanolamine dissolved in ethanol having an acid phosphate of chromium dissolved therein, said solution being at a pH between 0.5 and 3. This solution is capable of combining with rust or scale with out notably attacking the underlying metal. The acid phosphate in this solution is the descaling and derusting agent and in addition, a passivating agent for the metal. The hydroylsis of the acid phosphate of chromium and of triethanolamine precipitates a basic double phosphate of chromium and of triethanolamine, which acts as a protector against corrosion. phosphate is brought about simply by washing off with water of the solution adhering to the metal, the metal having been degreased and derusted by the action of this solution.

The solution of the chromium acid phosphate with an The hydrolysis of the acid ethanolamine such as triethanolamine, in a water-miscible organic solvent such as alcohol or pyridine can be applied to the metal article under treatment, by means of a brush, sponge, rag, etc. The surface tension of the solutan is below that of oil which causes the solution to easily penetrate into all the irregularities of the surface of the metal under treatment. The solution penetrates even un' der old paint, which is not too firmly adherent to the underlying metal. It also attacks all rust and scale thereby permitting easy washing in cases where the articles are to be repainted at once in the usual manner.

The degreasing is effected very rapidly, requiring only a minute or so when accompanied by some mechanical effort such as brushing or rubbing with a sponge. The duration of the derusting or descaling is variable dependng on the depth of the rust or the depth of the oxidation of the aluminum in cases where aluminum is the underlying metal. The time for this descaling may vary from a minute to an hour. If the amount of rust or oxidation is great, and if one proceeds by application of the liquid by brush or sponge, the same treatment can be repeated several times. Even in such case, where the treatment is repeated a number of times, the amount of the composition added may represent stoichiometrically less than the chemical equivalent of the rust to be dissolved.

Due to the fact that phosphate of chromium cannot be easily bought in the market, in the preparation of this solution the chromium phosphate is prepared in the solution. It is possible, of course, to add the acid phosphate of chromium directly to the alcoholic solution of the ethanolamine but for the sake of economy, it is preferable to prepare it in the solution. To carry this out, therefore, phosphoric acid is first mixed with the water-miscible organic solvent. Chromie acid is then added to the so lution. In cases where the water-miscible organic solvent is an alcohol, such as ethanol, the chromic acid is reduced by some of the ethanol to form the green oxide of chromium Cr (OH)3 plus an aldehyde such as acetal. it can be seen from the above that where it is desired to produce the phosphate of chromium in the solution the water-miscible organic solvent used would have to be a reducing agent such as an alcohol.

The green oxide of chromium combines With the phosphoric acid and triethanolamine to form soluble acid phosphate of chromium and triethanolamine. The aldehyde evaporates because the reaction is very exothermic. It is necessary therefore, to add the chromic acid very slowly, down the sides of the vessel at the same time keeping the solution cold, and it is for this reason that it is preferable to first add the phosphoric acid to the alcohol so that all the reactions (reduction of the chromic acid in combination with the green oxide of chromium with phosphoric acid) will occur progressively. The step in the process at which the ethanolamine (preferably tri or poly) is added, makes very little difference. Practically it is added and mixed with the alcohol, to which the phosphoric acid is added and then the chromic acid solution is added.

The reason for the use of chromic acid in aqueous solution is to avoid too great a rise in temperature. The alcohol will take fire from the high temperature and will burn even in water. As previously stated, the addition of the chromic acid is carried on While the vessel is kept in an ice bath. Moreover, it is necessary to avoid an excess of alcohol so as to keep to a minimum the in flammable vapors.

it is also possible to dissolve the oxide of chromium in phosphoric acid to obtain the phosphate of chromium. When the phosphate of chromium is made all of the chromic acid is reduced to the state of chromium salts, thereby enabling us to first make the phosphate of chromium and add that to the solution. it is not therefore necessary to follow the exact sequence of steps of first adding phosphoric acid to the solution and then ehrotnic .5 acid to this solution. However, for convenience the chromic acid is added to the solution containing the phosphoric acid and an ethanolamine, which ethanolamine has formed with the phosphoric acid an acid phosphate of the ethanolamine.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, as to the product and the processes for producing the product, together with additional objects and advantages thereof, will be best understood from the following specific examples. These examples are illustrative only and are not meant in any way to limit the scope of the invention.

Example 1 To a mixture of 1 kg. of ethanol (of say 95% strength) and 0.25 kg. of pyridine there is added 0.125 kg. of triethanolamine. The components are well agitated to obtain a uniform mixture. There is then slowly added 1.9 kg. of phosphoric acid having a specific gravity of 1.6 corresponding to about 1.2 kg. of actual phosphoric acid, H3PO4. There is at first precipitated a basic phosphate of triethanolamine which dissolves later as the acid phosphate. There is then added slowly, with good agitation, a solution of 60 grams of chromic acid in 120 cc. of water, to this solution while said solution is kept cold. A violent exothermic reaction takes place which is the reason the solution is kept cold. Chromic oxide, CrOa, is transformed to the reduced form Crz'Os, some of the ethanol being oxidized to the acetal. The strong cooling of the reacting mixture prevents undue waste of the alcohol from the heat of reaction. Without this cooling the waste of alcohol would be considerable. The resulting solution, having a weight of 3.1 kg., contains a double acid phosphate of chromium and triethanolamine together with some phosphoric acid, alcohol, and acetal. This solution has a pH of about 2.5 and the specific gravity-of 1.25.

Example 2 To 1 kg. of ethanol 95%, there is added 0.15 kg. of triethanolamine. Separately 2 kg. of phosphoric acid having a specific gravity of 1.6 (corresponding to about 1.2 kg. of actual phosphoric acid, H3PO4) are mixed with 45 grams of CrOs and 30 grams of zinc carbonate. The second solution is added to the first solution slowly While cooling. CrOa is reduced to CrzOs, which reacts, and goes into solution. After the solution has been well cooled 3 kg. of water may be added. The resulting solution has a pH of 2.85, a weight of 6.5 kg. and a specific gravity of about 1.12.

Example 3 Example 4 To 1 kg. of isopropyl alcohol and .3 kg. of methanol is added .2 kg. of diethanolarnine. To this is added 2.5 kg. of phosphoric acid of 1.6 specific gravity. Then, slowly and while being kept cold, as in the previous examples, is added 70 grams of chromic acid dissolved in 150 cc. of water. 1.2.

Example 5 To 1 kg. of propyl alcohol is added 180 grams of mono: ethanolamine and 1.5 kg. of phosphoric acid at a Specific gravity 1.6. To this is added '100 grams of chromi'ciacid dissolved in 200 cc. of water, the addition being slow The final solution thus obtained has a pH of 6 and the solutions kept cold as in previous examples. The pH of the solution is 2.9.

Example 6 To l-kg. of pyridine is added 250 grams of triethanolamine. To this is added 3 kg. of phosphoric acid of a density of 1.6. Taking the same precautions as in the previous examples, 150 grams of chromic acid dissolved in 200 cc. of water is added to this solution slowly while the1 solution is kept cold. The pH of the final solution is .2.

Example 7 To .5 kg. of pyridine and .5 kg. of isopropyl alcohol is added 150 grams of polyethanolamine. 200 grams of phosphoric acid is added and to this entire mass is added 200 grams of chromic acid dissolved in 250 cc. of water. The method of additions and precautions are exactly identical with those of the previous examples. The pH of the final solution is 2.2.

Example 8 By the same method as in the previous examples a solution is made of the following: 0.5 kg. of methanol, 0.8 kg. of propyl alcohol, grams of triethanolamine, 500 grams of phosphoric acid, and 250 grams of chromic acid dissolved in 250 cc. of water. The pH of the final solution is 1.6.

It is possible within the scope of this invention to add additional substances to the solution which might aid in the preparation of the metal products for coating etc. Such substances might, for example be an abrasive such as tripoli, etc., which is commonly used in scouring powders.

As shown by the table containing preferred limits of concentrations, the proportions and the concentrations of the reactants can be varied between rather wide limits. It is always, however, kept within such limits as to yield a final pH between 0.5 and 3.0 at the end of the process.

The solutions produced will mix in all proportions with water. This is a very desirable quality and can only be done by the use of water-miscible organic solvents as previously stated.

If it is desired simply to degrease, derust or descale and to protect the *metal pieces without any further treatment such as painting, varnishing, coating or plating, etc., it is suflicient to treat the metal pieces one or more times with the solutions prepared as herein described. The metal pieces are then dried with the same solution, or the reaction products of this solution with the rust, etc., on their surfaces. The white film obtained by washing the metal pieces with the solution is composed of a triple phosphate of chromium, triethanolamine and iron. in effect, the phosphoric acid liberated having reacted with the oxides or iron constituting the rust form a phosphate of iron which is finally mixed with a phosphate of chromium and the triethanolarnine in the white layer obtained after the washing.

/ If degreasing, descaling and derusting and passivation of the metal pieces are desired, followed by some further treatment i. e. painting, varnishing, lacquering, plating with another metal by electro-deposit on anodic oxidation, galvano-plastic deposition, galvanizing or the like, the metal pieces are treated with an excess of the acid cleaning solution, brushing or scrubbing with wire brushes if desired, followed by washing and drying.

The invention is also applicable to the treatment of various industrial metal products, i. e. copper, brass or other alloys or copper, etc., with the object of producing a protective coating of double phosphatev of chromium and an ethanolarnine.

It will be understood that each of the elements described above, or two or more together, may alsofi'nd a useful application in other types of solutions differing from the types described above.

While the invention has been illustrated and described as embodied in the foregoing examples, it is not intended to be limited to the details shown, since various modifications may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with water in all proportions in a concentration of -20% of said aqueous solution; and of at least one complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

2. A product useful in the preparation of metallic sur faces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with water in all proportions selected from the group consisting of methyl alcohol, ethyl alcohol, glycerine, propyl alcohol and isopropyl alcohol in a concentration of 5-20% of said aqueous solution; and of at least one complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is be tween 0.5-3.0.

3. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of pyridine miscible with water in all proportions in a concentration of 520% of said aqueous solution; and of at least one complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

4. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with water in all proportions in a concentration of 5-20% of said aqueous solution, sutiicient to degrease the metallic surface to which said product is applied; and of at least one complex double acid phosphate salt of at least one ethanolamine selected from the group consisting of monoethanolamine, diethanolamine and triethanolarnine, and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

5. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with water in all proportions selected from the group consisting of methyl alcohol, ethyl alcoiol, glycerine, propyl alcohol and isopropyl alcohol in a concentration of 5-20% of said aqueous solution, sutiicient to degrease the metallic surface to which said product is applied; and of at least one complex double acid phosphate salt of at least one ethanolamine selected from the group consisting of monoethanolamine, diethanolarnine and triethanolamine, and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

6. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of pyridine miscible with water in all proportions in a concentration of 5-20% of said aqueous solution, sufiicient to degrease the metallic surface to which said product is applied; and of at least one complex double acid phosphate salt of at least one ethanolamine selected from the group consisting of monoethanolamine, diethano-lamine, triethanolamine, and chromium and the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

7. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with Water in all proportions in a concentration of 5-20% of said aqueous solution; and of a complex double acid phosphate salt of triethanolarnine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

8. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with water in all proportions in a concentration of 5-20% of said aqueous solution, sufficient to degrease the metallic surface to which said product is applied; and of. a complex double acid phosphate salt of at least one ethanolamine and chromium and zinc, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

9. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of a concentrated aqueous solution of 5-20% of at least one organic grease solvent miscible with water in all proportions; and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the concentration in said solution of phosphate ion being between 10-60%, of ethanolamine between 1-5% and of chromic ion between 1-5%, the pH of said concentrated aqueous solution being between 0.5-3.0.

10. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of a concentrated aqueous solution of 10% of at least one organic grease solvent miscible with water in all proportions; and of a complex double acid phosphate salt of at least one ethanolarnine and chromium, the concentration in said solution of phosphate ion being between l060%, of ethanolamine between 1-5% and of chromic ion between 1-5 the pH of said concentrated aqueous solution being between 0.5-3.0.

11. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of a concentrated aqueous solution of 10% of at least one organic grease solvent miscible with water in all proportions; and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the concentration in said solution of phosphate ion being about 20%, of ethanolamine about 1-5 and of chromic ion between 1-5 the pH of said concentrated aqueous solution being between 0.5-3.0.

12. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of a concentrated aqueous solution of 10% of at least one organic grease solvent miscible with water in all. proportions; and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the concentration in said solution of phosphate ion being about 20%, of ethanolamine about 2% and of chromic ion about 2%, the pH of said concentrated aqueous solution being between 0.5-3.0.

13. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of an acetal miscible with water in all proportions in a concentration of -20% of said aqueous solution; and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0.

14. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of a concentrated aqueous solution of a complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said concentrated aqueous solution is between 0.5-3.0.

15. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the step of applying to the surface of a metal article to be treated an aqueous solution of at least one organic solvent miscible with water in all proportions in a concentration of 5-20% of said aqueous solution; and of a complex double acid phosphate salt of at least one ethanolamine and chromium,

" the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.53.0; and removing said aqueous solution and loose dirt from the surface of said metal article.

16. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the steps of applying to the surface of a metal article to be treated an aqueous solution of at least one organic grease solvent miscible with water in all proportions selected from the group consisting of methyl alcohol, ethyl alcohol, glycerine, propyl alcohol and isopropyl alcohol in a concentration of 5-20% of said aqueous solution; and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0; and removing said aqueous solution and loose dirt from the surface of said metal article, thereby obtaining a metal article ready for coating.

17. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the steps of applying to the surface of a metal article to be treated an aqueous solution of pyridine miscible with water in all proportions in a concentration of 520% of said aqueous solution, and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0; and removing said aqueous solution and loose dirt from the surface of said metal article, thereby obtaining a metal article ready for coating.

18. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the steps of applying to the surface of a metal article to be treated an aqueous solution of at least one organic grease solvent miscible with water in all proportions in a concentration of 5-20% of said aqueous solution, and of a complex double acid phosphate salt of at least one ethanolamine selected from the group consisting of monoethanolamine, diethanolamine and triethanolamine, and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0; and removing said aqueous solution and loose dirt from the surface of said metal 10 article, thereby obtaining a metal article ready for coatmg.

19. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the steps of applying to the surface of a metal article to be treated an aqueous solution of at least one organic grease solvent miscible with water in all proportions in a concentration of 520% of said aqueous solution, and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 0.5-3.0; rubbing said aqueous solution on the surface of said metal article so as to loosen attached dirt; and removing said aqueous solution and loose dirt from the surface of said metal article, thereby obtaining a metal article ready for coating.

20. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the steps of applying to the surface of a metal article to be treated an aqueous solution of 520% of at least one organic grease solvent miscible with water in all proportions, and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the concentration in said solution of phosphate ion being between 10-60%, of ethanolamine between 1-5%, and of chromic ion between 1-5%, the pH of said concentrated aqueous solution being between 0.5- 3.0; and removing said aqueous solution and loose dirt from the surface of said metal article, thereby obtaining a metal article ready for coating.

21. In a process of treating a metallic article carrying greasy matter and corrosion on its surface to prepare the same for coating, the steps of applying to the surface of a metal article to be treated an aqueous solution of 10% of at least one organic grease solvent miscible with water in all proportions, and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the concentration in said solution of phosphate ion being about 20%, of ethanolamine about 2%, and of chromic ion about 2%, the pH of said concentrated aqueous solution being between 0.5-3.0; and removing said aqueous solution and loose dirt from the surface of said metal article, thereby obtaining a metal article ready for coating.

22. A product useful in the preparation of metallic surfaces for coating, said product consisting essentially of an aqueous solution of at least one organic grease solvent miscible with water in all proportions in a concentration of 520% of said aqueous solution; and of a complex double acid phosphate salt of at least one ethanolamine and chromium, the amount of phosphate of said complex double acid phosphate salt being so adjusted that the pH of said aqueous solution is between 1-2.5.

References Cited in the file of this patent UNITED STATES PATENTS 1,665,465 Klinger et al. Apr. 10, 1928 1,678,775 Gravell July 31, 1928 1,735,842 Allen Nov. 19, 1929 1,936,533 Albrecht Nov. 21, 1933 2,298,280 Clifford et al. Oct. 13, 1942 2,318,606 Goebel May 11, 1943 2,328,540 Hochwalt Sept. 7, 1943 2,385,800 Douty et a1. Oct. 2, 1945 2,408,155 Thornbury Sept. 24, 1946 2,418,608 Thompson et al. Apr. 8, 1947 2,456,947 Jernstedt Dec. 21, 1948 

1. A PRODUCT USEFUL IN THE PREPARATION OF METALLIC SURFACES FOR COATING, SAID PRODUCT CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF AT LEAST ONE ORGANIC GREASE SOLVENT MISCIBLE WITH WATER IN ALL PROPORTIONS IN A CONCENTRATION OF 5-20% OF SAID AQUEOUS SOLUTION; AND OF AT LEAST ONE COMPLEX DOUBLE ACID PHOSPHATE SALT OF AT LEAST ONE ETHANOLAMINE AND CHROMIUM, THE AMOUNT OF PHOSPHATE OF SAID COMPLEX DOUBLE ACID PHOSPHATE SALT BEING SO ADJUSTED THAT THE PH OF SAID AQUEOUS SOLUTION IS BETWEEN 0.5-3.0.
 15. IN A PROCESS OF TREATING A METALLIC ARTICLE CARRYING GREASY MATTER AND CORROSION ON ITS SURFACE TO PREPARE THE SAME FOR COATING, THE STEP OF APPLYING TO THE SURFACE OF A METAL ARTICLE TO THE TREAED AN AQUEOUS SOLUTION OF AT LEAST ONE ORGANIC SOLVENT MISCIBLE WITH WATER IN ALL PROPORTIONS IN A CONCENTRATION OF 5-20% OF SAID AQUEOUS SOLUTION; AND OF A COMPLEX DOUBLE ACID PHOSPHATE SALT OF AT LEAST ONE ETHANOLAMINE AND CHROMIUM, THE AMOUNT OF PHOSPHATE OF SAID COMPLEX DOUBLE ACID PHOSPHATE SALT BEING SO ADJUSTED THAT THE PH OF SAID AQUEOUS SOLUTION IS BETWEEN 0.5-3.0; AND REMOVING SAID AQUEOUS SOLUTION AND LOOSE DIRT FROM THE SURFACE OF SAID METAL ARTICLE. 